A theoretical approach based on electromagnetic scattering for analysing dielectric shimming in high-field MRI
A theoretical approach based on electromagnetic scattering for analysing dielectric shimming in high-field MRI
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DOI：
10.1002/mrm.25783
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发表时间：
2016-05-01
影响因子：
3.3
通讯作者：
Webb, Andrew G.
中科院分区：
文献类型：
--
作者：
Brink, Wyger M.;Remis, Rob F.;Webb, Andrew G.
目的利用积分方程将电介质闪变问题表述为电磁散射问题，对其进行分析。方法从感应电流和二次场的角度对两种不同材料结构下的射频场进行三维模拟分析。采用不同背景下的二维积分方程方法对其物理机制进行了识别。该框架随后被用于开发介电垫设计的反演方法。结果介电垫的影响可归因于介电垫中感应电流产生的二次场的干扰，该二次场在非均匀背景下辐射。非齐次背景下的积分方程法大大降低了正反问题的复杂性，可用于优化理想B-1（+）场的介电常数分布。在圆柱形模型中得到了与实验B-1（+）图一致的结果，证明了该方法的有效性。结论非均匀背景下的积分方程法为介质闪光材料的分析和反设计提供了一个有效的数值框架。中华医学杂志，2016,25(5):559 - 564。(c) 2015 Wiley期刊公司
PurposeIn this study, we analyzed dielectric shimming by formulating it as an electromagnetic scattering problem using integral equations.MethodsThree-dimensional simulations of the radiofrequency field in two configurations using different materials were analyzed in terms of induced currents and secondary fields. A two-dimensional integral equation method with different backgrounds was used to identify the underlying physical mechanisms. This framework was then used to develop an inversion method for the design of dielectric pads.ResultsThe effects of a dielectric pad can be attributed to the interference of a secondary field that is produced by the currents induced in the dielectric pad, radiating in an inhomogeneous background. The integral equation method with inhomogeneous background reduces the complexity of the forward and inverse problem significantly and can be used to optimize the permittivity distribution for a desired B-1(+) field. Agreement with experimental B-1(+) maps was obtained in a cylindrical phantom, demonstrating the validity of the method.ConclusionsThe integral equation method with inhomogeneous background yields an efficient numerical framework for the analysis and inverse design of dielectric shimming materials. Magn Reson Med 75:2185-2194, 2016. (c) 2015 Wiley Periodicals, Inc.